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About These Photographic Images

Overview

All of the photographs presented on the continuousWavewebsite were generally taken and prepared in the following manner:

A 35 mm SLR camera was used to expose Kodak "Royal Gold" Film;
Exposed film was professionally processed by a Kodak lab, and
The negatives were transferred to Photo-CD;
The PhotoCD images were opened in PhotoShop
Photoshop was used to adjust the image;
The modified image was saved as an 8-bit GIF or a 24-bit JPEG file.

Variations in Displays

Hardware and software variables can cause differences in the appearance of these images. There are two areas of concern: color resolution and gamma compensation.

Color Resolution

Depending on your video display hardware, you may be limited in the number of colors that your monitor can display. If your hardware can display at least 16-bit color ("thousands"), you should be able to get very good display of the images. You may notice some banding in the sky regions of the photographs. If you display on devices with less than 16-bit color, you may notice considerable change in the color. Even if you have a 16-bit or more capable display, there may be a problem due to variation in gamma compensation.

Gamma Compensation

The values contained in computer-graphics files (for the various pixels of color and luminance) are absolute values and are generally not the actual values used when the image is applied to a display device. In the process of displaying a computer-graphic image, each display device must apply some compensation to these values. This is because each device has fundamental non-linearities in the way it translates file representations of luminance and color values into actual displayed images of color and luminance.

In particular, video display devices have a very non-linear transfer. To compensate, a correction is applied called "gamma". The gamma correction affects the lower light regions the most. The subject of gamma compensation is a complex one and seems little understood by most computer graphics users. However, it can be said that under different operating systems, the apparent gamma correction can vary considerably. In short, this may cause the photographs to appear darker on your monitor than they do on my monitor, where exposure compensation was originally done.

For a complete discussion of monitor gamma, please read:

"Why Do Images Appear Darker on Some Displays?"
An Explanation of Monitor Gamma by
Robert W. Berger.

Charles A. Poynton has also assembled a great deal of information concerning the reproduction of color images on CRT displays and other devices.

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Last modified: Saturday, 25-Dec-1999 12:13:23 EST
Author: James W. Hebert